We are trying to study the binding sites for both nucleotide and aminoacyl tRNAs on elongation factor Tu by magnetic resonance methods. We are interested in both the origins of specificity and the spatial arrangements of binding sites. The environment of the nucleotide bound to elongation factor Tu will be studied by 31P NMR. This will include studies of the effect of pH on the chemical shift and the effect of paramagnetic metal ions on a spin label covalently attached to the reactive thiol group. The synthesis of 13C GDP will be carried out, and the complex with elongation factor Tu will be studied by 13C NMR. Elongation factor Ts will be isolated and used to increase the rate of the exchange of nucleotide with elongation factor Tu as its GDP complex in order to allow direct measurement of relative equilibrium constants by NMR.